Category Archives: Physics

China launches quantum satellite for ‘hack-proof’ communications

The Guardian reports: China says it has launched the world’s first quantum satellite, a project Beijing hopes will enable it to build a coveted “hack-proof” communications system with potentially significant military and commercial applications.

Xinhua, Beijing’s official news service, said Micius, a 600kg satellite that is nicknamed after an ancient Chinese philosopher, “roared into the dark sky” over the Gobi desert at 1.40am local time on Tuesday, carried by a Long March-2D rocket.

“The satellite’s two-year mission will be to develop ‘hack-proof’ quantum communications, allowing users to send messages securely and at speeds faster than light,” Xinhua reported.

The Quantum Experiments at Space Scale, or Quess, satellite programme is part of an ambitious space programme that has accelerated since Xi Jinping became Communist party chief in late 2012.

“There’s been a race to produce a quantum satellite, and it is very likely that China is going to win that race,” Nicolas Gisin, a professor and quantum physicist at the University of Geneva, told the Wall Street Journal. “It shows again China’s ability to commit to large and ambitious projects and to realise them.”

The satellite will be tasked with sending secure messages between Beijing and Urumqi, the capital of Xinjiang, a sprawling region of deserts and snow-capped mountains in China’s extreme west.

Highly complex attempts to build such a “hack-proof” communications network are based on the scientific principle of entanglement. [Continue reading…]

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Physicists undiscover ‘new particle’

Discover reports: What began as a bump has turned out to be nothing more than a statistical ghost.

Physicists at the International Conference on High Energy Physics in Chicago announced today that the much-discussed 750 GeV aberration in their data discovered by the Large Hadron Collider at the end of last year disappeared upon further testing.

“There is no excess seen in the 2016 data particularly around 750 GeV, confirms Bruno Lenzi, a physicist at CERN. “All over the mass range the data is consistent with the background only hypothesis.”

It was thought that the bump indicated the presence of a much larger particle new to physics, which could have held exciting implications for everything from the search for dark matter to quantum gravity. [Continue reading…]

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Neutrinos and antineutrinos hint at an answer to one of the biggest questions in physics

Natalie Wolchover writes: In the same underground observatory in Japan where, 18 years ago, neutrinos were first seen oscillating from one “flavor” to another — a landmark discovery that earned two physicists the 2015 Nobel Prize — a tiny anomaly has begun to surface in the neutrinos’ oscillations that could herald an answer to one of the biggest mysteries in physics: why matter dominates over antimatter in the universe.

The anomaly, detected by the T2K experiment, is not yet pronounced enough to be sure of, but it and the findings of two related experiments “are all pointing in the same direction,” said Hirohisa Tanaka of the University of Toronto, a member of the T2K team who presented the result to a packed audience in London earlier this month.

“A full proof will take more time,” said Werner Rodejohann, a neutrino specialist at the Max Planck Institute for Nuclear Physics in Heidelberg who was not involved in the experiments, “but my and many others’ feeling is that there is something real here.”

The long-standing puzzle to be solved is why we and everything we see is matter-made. More to the point, why does anything — matter or antimatter — exist at all? The reigning laws of particle physics, known as the Standard Model, treat matter and antimatter nearly equivalently, respecting (with one known exception) so-called charge-parity, or “CP,” symmetry: For every particle decay that produces, say, a negatively charged electron, the mirror-image decay yielding a positively charged antielectron occurs at the same rate. But this cannot be the whole story. If equal amounts of matter and antimatter were produced during the Big Bang, equal amounts should have existed shortly thereafter. And since matter and antimatter annihilate upon contact, such a situation would have led to the wholesale destruction of both, resulting in an empty cosmos.

Somehow, significantly more matter than antimatter must have been created, such that a matter surplus survived the annihilation and now holds sway. The question is, what CP-violating process beyond the Standard Model favored the production of matter over antimatter? [Continue reading…]

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A stunning prediction of climate science — and basic physics — may now be coming true

The Washington Post reports: A lot of people deny climate change. Not many, though, deny gravity.

That’s why a recent animation released by NASA’s Jet Propulsion Laboratory — well, it came out in April, but people seem to be noticing it now — is so striking. Because it suggests the likely gravitational imprint of our changing climate on key features of the Earth in a way that’s truly startling.

The animation uses measurements from NASA’s squadron of GRACE satellites (Gravity Recovery and Climate Experiment), which detect changes in mass below them as they fly over the Earth, to calculate how the ocean changed from April 2002 until July 2013, based on corresponding changes in the mass of the continents. The resulting animation suggests the oceans gained mass overall, as seas rose, albeit with seasonal variations that result from water moving from the continents into the seas and back again.

But in key areas where glaciers have been melting — coastal Alaska, West Antarctica and, above all, Greenland — it suggests something very different happened. Here, the animation finds that the ocean actually fell, and in some places by as much as 50 millimeters (2 inches) over this short decadal span: [Continue reading…]

 

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Jupiter is a garden of storms

 

Brian Gallagher writes: It’s always a mistake to read,” Philip Marcus, a computational physicist and a professor in the mechanical engineering department at the University of California, Berkeley, tells me in a coffee shop near campus. “You learn too many things. That’s how I got really fascinated by fluid dynamics.”

It was 1978, and Marcus was in his first year of a post-doctoral position at Cornell focused on numerical simulations of solar convection and laboratory flows using spectral methods. But he had wanted to study cosmic evolution and general relativity; the problem, as Marcus told me, was that there was talk of no one seeing results of general relativity within their lifetime. As a result, “the field kind of collapsed on itself a little bit, and so everybody from general relativity was going to other fields.”

It was also in 1978 that Voyager 1 began to send up-close images of Jupiter back to Earth. When Marcus needed to, as he put it, “unwind, relax, whatever,” he would walk over to a special library, next to the astrophysics building, and marvel at Voyager’s images of the Great Red Spot. The storm had raged hundreds of millions of miles away since at least 1665, when it was first observed by Robert Hooke. “I realized that almost nobody in astronomy was trained in fluid dynamics, and I was,” he told me. “And I said, well, I’m in as good a position as anybody to start studying this.”

And he never stopped. Today, he is something of an expert on the solar system’s most famous storm. Sporting a mountain-biker’s build, he answered my questions with animation, often waving his hands around to clarify his concepts. He admitted this energy of his could encourage clumsiness. “People are leery of me,” he said. “If I walked into a laboratory, I would immediately break everything.” Thankfully, he explained, “I have the great fortune of having some wonderful friends who are experimentalists.” [Continue reading…]

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Second gravitational wave detected from ancient black hole collision

The Guardian reports: Physicists have detected ripples in the fabric of spacetime that were set in motion by the collision of two black holes far across the universe more than a billion years ago.

The event marks only the second time that scientists have spotted gravitational waves, the tenuous stretching and squeezing of spacetime predicted by Einstein more a century ago.

The faint signal received by the twin instruments of the Laser Interferometer Gravitational Wave Observatory (LIGO) in the US revealed two black holes circling one another 27 times before finally smashing together at half the speed of light. [Continue reading…]

 

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Yes, there have been aliens

Adam Frank writes: Last month astronomers from the Kepler spacecraft team announced the discovery of 1,284 new planets, all orbiting stars outside our solar system. The total number of such “exoplanets” confirmed via Kepler and other methods now stands at more than 3,000.

This represents a revolution in planetary knowledge. A decade or so ago the discovery of even a single new exoplanet was big news. Not anymore. Improvements in astronomical observation technology have moved us from retail to wholesale planet discovery. We now know, for example, that every star in the sky likely hosts at least one planet.

But planets are only the beginning of the story. What everyone wants to know is whether any of these worlds has aliens living on it. Does our newfound knowledge of planets bring us any closer to answering that question?

A little bit, actually, yes. In a paper published in the May issue of the journal Astrobiology, the astronomer Woodruff Sullivan and I show that while we do not know if any advanced extraterrestrial civilizations currently exist in our galaxy, we now have enough information to conclude that they almost certainly existed at some point in cosmic history. [Continue reading…]

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Universe is expanding up to 9% faster than we thought, say scientists

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The Guardian reports: The universe is expanding faster than anyone had previously measured or calculated from theory. This is a discovery that could test part of Albert Einstein’s theory of relativity, a pillar of cosmology that has withstood challenges for a century.

Nasa and the European Space Agency jointly announced the universe is expanding 5% to 9% faster than predicted, a finding they reached after using the Hubble space telescope to measure the distance to stars in 19 galaxies beyond theMilky Way.

The rate of expansion did not match predictions based on measurements of radiation left over from the Big Bang that gave rise to the known universe 13.8bn years ago.

Physicist and lead author Adam Riess said: “You start at two ends, and you expect to meet in the middle if all of your drawings are right and your measurements are right.

“But now the ends are not quite meeting in the middle and we want to know why.” [Continue reading…]

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New support for an alternative formulation of quantum mechanics

Dan Falk writes: Of the many counterintuitive features of quantum mechanics, perhaps the most challenging to our notions of common sense is that particles do not have locations until they are observed. This is exactly what the standard view of quantum mechanics, often called the Copenhagen interpretation, asks us to believe. Instead of the clear-cut positions and movements of Newtonian physics, we have a cloud of probabilities described by a mathematical structure known as a wave function. The wave function, meanwhile, evolves over time, its evolution governed by precise rules codified in something called the Schrödinger equation. The mathematics are clear enough; the actual whereabouts of particles, less so. Until a particle is observed, an act that causes the wave function to “collapse,” we can say nothing about its location. Albert Einstein, among others, objected to this idea. As his biographer Abraham Pais wrote: “We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it.”

But there’s another view — one that’s been around for almost a century — in which particles really do have precise positions at all times. This alternative view, known as pilot-wave theory or Bohmian mechanics, never became as popular as the Copenhagen view, in part because Bohmian mechanics implies that the world must be strange in other ways. In particular, a 1992 study claimed to crystalize certain bizarre consequences of Bohmian mechanics and in doing so deal it a fatal conceptual blow. The authors of that paper concluded that a particle following the laws of Bohmian mechanics would end up taking a trajectory that was so unphysical — even by the warped standards of quantum theory — that they described it as “surreal.”

Nearly a quarter-century later, a group of scientists has carried out an experiment in a Toronto laboratory that aims to test this idea. And if their results, first reported earlier this year, hold up to scrutiny, the Bohmian view of quantum mechanics — less fuzzy but in some ways more strange than the traditional view — may be poised for a comeback.

Bohmian mechanics was worked out by Louis de Broglie in 1927 and again, independently, by David Bohm in 1952, who developed it further until his death in 1992. (It’s also sometimes called the de Broglie–Bohm theory.) As with the Copenhagen view, there’s a wave function governed by the Schrödinger equation. In addition, every particle has an actual, definite location, even when it’s not being observed. Changes in the positions of the particles are given by another equation, known as the “pilot wave” equation (or “guiding equation”). The theory is fully deterministic; if you know the initial state of a system, and you’ve got the wave function, you can calculate where each particle will end up.

That may sound like a throwback to classical mechanics, but there’s a crucial difference. Classical mechanics is purely “local” — stuff can affect other stuff only if it is adjacent to it (or via the influence of some kind of field, like an electric field, which can send impulses no faster than the speed of light). Quantum mechanics, in contrast, is inherently nonlocal. The best-known example of a nonlocal effect — one that Einstein himself considered, back in the 1930s — is when a pair of particles are connected in such a way that a measurement of one particle appears to affect the state of another, distant particle. The idea was ridiculed by Einstein as “spooky action at a distance.” But hundreds of experiments, beginning in the 1980s, have confirmed that this spooky action is a very real characteristic of our universe.

In the Bohmian view, nonlocality is even more conspicuous. The trajectory of any one particle depends on what all the other particles described by the same wave function are doing. And, critically, the wave function has no geographic limits; it might, in principle, span the entire universe. Which means that the universe is weirdly interdependent, even across vast stretches of space. The wave function “combines — or binds — distant particles into a single irreducible reality,” as Sheldon Goldstein, a mathematician and physicist at Rutgers University, has written. [Continue reading…]

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Why physics is not a discipline

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Philip Ball writes: Have you heard the one about the biologist, the physicist, and the mathematician? They’re all sitting in a cafe watching people come and go from a house across the street. Two people enter, and then some time later, three emerge. The physicist says, “The measurement wasn’t accurate.” The biologist says, “They have reproduced.” The mathematician says, “If now exactly one person enters the house then it will be empty again.”

Hilarious, no? You can find plenty of jokes like this — many invoke the notion of a spherical cow — but I’ve yet to find one that makes me laugh. Still, that’s not what they’re for. They’re designed to show us that these academic disciplines look at the world in very different, perhaps incompatible ways.

There’s some truth in that. Many physicists, for example, will tell stories of how indifferent biologists are to their efforts in that field, regarding them as irrelevant and misconceived. It’s not just that the physicists were thought to be doing things wrong. Often the biologists’ view was that (outside perhaps of the well established but tightly defined discipline of biophysics) there simply wasn’t any place for physics in biology.

But such objections (and jokes) conflate academic labels with scientific ones. Physics, properly understood, is not a subject taught at schools and university departments; it is a certain way of understanding how processes happen in the world. When Aristotle wrote his Physics in the fourth century B.C., he wasn’t describing an academic discipline, but a mode of philosophy: a way of thinking about nature. You might imagine that’s just an archaic usage, but it’s not. When physicists speak today (as they often do) about the “physics” of the problem, they mean something close to what Aristotle meant: neither a bare mathematical formalism nor a mere narrative, but a way of deriving process from fundamental principles.

This is why there is a physics of biology just as there is a physics of chemistry, geology, and society. But it’s not necessarily “physicists” in the professional sense who will discover it. [Continue reading…]

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How do we know the distance to the stars?

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Exploration is in our nature. We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars. — Carl Sagan

Ethan Siegel writes: To look out at the night sky and marvel at the seemingly endless canopy of stars is one of the oldest and most enduring human experiences we know of. Since antiquity, we’ve gazed towards the heavens and wondered at the faint, distant lights in the sky, curious as to their nature and their distance from us. As we’ve come to more modern times, one of our cosmic goals is to measure the distances to the faintest objects in the Universe, in an attempt to uncover the truth about how our Universe has expanded from the Big Bang until the present day. Yet even that lofty goal depends on getting the distances right to our nearest galactic neighbors, a process we’re still refining. We’ve taken three great steps forward in our quest to measure the distance to the stars, but we’ve still got further to go.

The story starts in the 1600s with the Dutch scientist, Christiaan Huygens. Although he wasn’t the first to theorize that the faint, nighttime stars were Suns like our own that were simply incredibly far away, he was the first to attempt to measure their distance. An equally bright light that was twice as far away, he reasoned, would only appear one quarter as bright. A light ten times as distant would be just one hundredth as bright. And so if he could measure the brightness of the brightest star in the night sky  — Sirius  —  as a fraction of the brightness of the Sun, he could figure out how much more distant Sirius was than our parent star. [Continue reading…]

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The flow of time is central to human experience. Why isn’t it central to physics?

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Gene Tracy writes: The flow of time is certainly one of the most immediate aspects of our waking experience. It is essential to how we see ourselves and to how we think we should live our lives. Our memories help fix who we are; other thoughts reach forward to what we might become. Surely our modern scientific sense of time, as it grows ever more sophisticated, should provide meaningful insights here.

Yet today’s physicists rarely debate what time is and why we experience it the way we do, remembering the past but never the future. Instead, researchers build ever-more accurate clocks. The current record-holder, at the Joint Institute for Laboratory Astrophysics in Colorado, measures the vibration of strontium atoms; it is accurate to 1 second in 15 billion years, roughly the entire age of the known universe. Impressive, but it does not answer ‘What is time?’

To declare that question outside the pale of physical theory doesn’t make it meaningless. The flow of time could still be real as part of our internal experience, just real in a different way from a proton or a galaxy. Is our experience of time’s flow akin to watching a live play, where things occur in the moment but not before or after, a flickering in and out of existence around the ‘now’? Or, is it like watching a movie, where all eternity is already in the can, and we are watching a discrete sequence of static images, fooled by our limited perceptual apparatus into thinking the action flows smoothly?

The Newtonian and Einsteinian world theories offer little guidance. They are both eternalised ‘block’ universes, in which time is a dimension not unlike space, so everything exists all at once. Einstein’s equations allow different observers to disagree about the duration of time intervals, but the spacetime continuum itself, so beloved of Star Trek’s Mr Spock, is an invariant stage upon which the drama of the world takes place. In quantum mechanics, as in Newton’s mechanics and Einstein’s relativistic theories, the laws of physics that govern the microscopic world look the same going forward or backward in time. Even the innovative speculations of theorists such as Sean Carroll at Caltech in Pasadena – who conceives of time as an emergent phenomenon that arises out of a more primordial, timeless state – concern themselves more with what time does than what time feels like. Time’s flow appears nowhere in current theories of physics. [Continue reading…]

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Why our perceptions of an independent reality must be illusions

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Amanda Gefter writes: As we go about our daily lives, we tend to assume that our perceptions — sights, sounds, textures, tastes — are an accurate portrayal of the real world. Sure, when we stop and think about it — or when we find ourselves fooled by a perceptual illusion — we realize with a jolt that what we perceive is never the world directly, but rather our brain’s best guess at what that world is like, a kind of internal simulation of an external reality. Still, we bank on the fact that our simulation is a reasonably decent one. If it wasn’t, wouldn’t evolution have weeded us out by now? The true reality might be forever beyond our reach, but surely our senses give us at least an inkling of what it’s really like.

Not so, says Donald D. Hoffman, a professor of cognitive science at the University of California, Irvine. Hoffman has spent the past three decades studying perception, artificial intelligence, evolutionary game theory and the brain, and his conclusion is a dramatic one: The world presented to us by our perceptions is nothing like reality. What’s more, he says, we have evolution itself to thank for this magnificent illusion, as it maximizes evolutionary fitness by driving truth to extinction.

Getting at questions about the nature of reality, and disentangling the observer from the observed, is an endeavor that straddles the boundaries of neuroscience and fundamental physics. On one side you’ll find researchers scratching their chins raw trying to understand how a three-pound lump of gray matter obeying nothing more than the ordinary laws of physics can give rise to first-person conscious experience. This is the aptly named “hard problem.” [Continue reading…]

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Astronomers just saw farther back in time than they ever have before

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The Washington Post reports: To look through the lens of a telescope is to peer back in time.

The light we view through it has spent hundreds, millions, even billions of years crossing the vastness of space to reach us, carrying with it images of things that happened long ago.

On Thursday, astronomers at the Hubble Space Telescope announced that they’d seen back farther than they ever have before, to a galaxy 13.4 billion light years away in a time when the universe was just past its infancy.

The finding shattered what’s known as the “cosmic distance record,” illuminating a point in time that scientists once thought could never be seen with current technology.

“We’ve taken a major step back in time, beyond what we’d ever expected to be able to do with Hubble,” Yale University astrophysicist Pascal Oesch, the lead author of the study, said in a statement. [Continue reading…]

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Earth may be a 1-in-700-quintillion kind of planet

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Discovery Magazine reports: A new study suggests that there are around 700 quintillion planets in the universe, but only one like Earth. It’s a revelation that’s both beautiful and terrifying at the same time.

Astrophysicist Erik Zackrisson from Uppsala University in Sweden arrived at this staggering figure — a 7 followed by 20 zeros — with the aid of a computer model that simulated the universe’s evolution following the Big Bang. Zackrisson’s model combined information about known exoplanets with our understanding of the early universe and the laws of physics to recreate the past 13.8 billion years.

Zackrisson found that Earth appears to have been dealt a fairly lucky hand. In a galaxy like the Milky Way, for example, most of the planets Zackrisson’s model generated looked very different than Earth — they were larger, older and very unlikely to support life. The study can be found on the preprint server arXiv, and has been submitted to The Astrophysical Journal. [Continue reading…]

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Scientists glimpse Einstein’s gravitational waves

Phys.org reports: In a landmark discovery for physics and astronomy, scientists said Thursday they have glimpsed the first direct evidence of gravitational waves, ripples in the fabric of space-time that Albert Einstein predicted a century ago.

When two black holes collided some 1.3 billion years ago, the joining of those two great masses sent forth a wobble that hurtled through space and reached Earth on September 14, 2015, when it was picked up by sophisticated instruments, researchers announced.

“Up until now we have been deaf to gravitational waves, but today, we are able to hear them,” said David Reitze, executive director of the LIGO Laboratory, at a packed press conference in the US capital.

Reitze and colleagues compared the magnitude of the discovery to Galileo’s use of the telescope four centuries ago to open the era of modern astronomy.

“I think we are doing something equally important here today. I think we are opening a window on the universe,” Reitze said. [Continue reading…]

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Gravity waves can’t be understood without understanding Einstein’s idea of gravity

By David Blair, University of Western Australia

I have spent almost 40 years trying to detect gravity waves.

When I started there were just a few of us working away in university labs. Today 1,000 physicists working with billion-dollar observatories are quietly confident the waves are within our grasp.

If we are right, the gravity wave search will have taken 100 years from the date of Einstein’s prediction.

In 100 years’ time the discovery of Einstein’s gravity waves will be one of the landmarks in the history of science. It will stand out like the discovery of electromagnetic waves in 1886, a quarter of a century after these waves were predicted by physicist James Clerk Maxwell.

The problem of talking about gravity waves is that you can’t explain them without explaining Einstein’s idea of gravity. Recently I began to ask why it is so difficult to explain gravity, why the concept is met with glazed eyes and baffled looks. Eventually I came up with a theory I call the Tragedy of the Euclidean Time Warp.

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